(The following story by Rocco Parascandola appeared on Newsday’s website on April 29. Staff writers Joshua Robin and Curtis Taylor contributed to this story.)

NEW YORK -- Every train headed for Penn Station during this summer's four-day GOP convention will be stopped and searched by cops and bomb-sniffing dogs, Police Commissioner Ray Kelly announced yesterday -- an unprecedented plan likely to create a nightmare for millions of passengers on seven subway lines, two commuter trains and Amtrak.

Inconvenience aside, sources familiar with convention security plans say, Kelly believes it is the best way to prevent a terrorist attack.

"It's our goal to check every train, physically, with dogs and with police officers before it comes into Penn Station," Kelly said. "I think we're going to be well prepared."

About 500,000 passengers get on and off trains in Penn Station every day, riding the 1,9,2,3 or A,C,E subway lines; the LIRR or NJ Transit. Thousands more pass through on their way to other destinations.

Those assigned to search the trains in the initiative known as Train Order Maintenance Sweeps will be responsible for checking every car on every train.

Further logistics of the plan, such as where the trains will be checked along their routes, need to be finalized, sources said.

"The nitty-gritty has to be worked out," according to one source familiar with the security planning for the convention.

The source and others said it's conceivable certain subway stops could be skipped, as some were during Yankee ticker tape parades, or service disruptions could be more severe at key moments in the convention, such as when President George W. Bush addresses the crowd.

Kelly, speaking at an early morning forum at Baruch College, also stressed that there is no plan to close Penn Station, as some newspaper reports have suggested, although the decision lies ultimately with the Secret Service.

"It's never been discussed," Kelly said.

In Boston, where the Democratic Convention is being held July 26 to 29 in the FleetCenter, commuter trains will stop short of the nearby North Station, forcing 25,000 people a day to ride buses or subways into that city.

The Republican convention is to be held at Madison Square Garden, which sits atop Penn Station, from Aug. 30 through Sept. 2. It is considered a event terrorists would like to target.

With that in mind, the Police Department is in the midst of wide-ranging training against chemical, biological and radiological attacks. Upward of 10,000 cops - more than a quarter of the force - are expected to be assigned to the convention, sources say.

In addition to protecting dignitaries and politicians from across the country, the police must deal with protesters who could number as many as 250,000, by some predictions.

Peter Kalikow, chairman of the Metropolitan Transportation Authority, appeared to support the train-search plan.

"I'll leave it to the professionals, and they'll do what's necessary," he said. "Whatever is necessary to maintain security, we'll do."

MTA spokesman Tom Kelly said the police commissioner's announcement - the timing of which surprised some observers because it occurred at a rather low-key event - was something that had been talked about in recent weeks.

"We have ongoing discussions with the cops virtually every day," Tom Kelly said. "Any number of different scenarios are discussed, played out.

"This is not a surprise to us."

Mayor Michael Bloomberg said, as he often does, that he leaves security issues to Kelly.

"The Police Commissioner is the one that I look to to come up with a security plan to protect this city," he said at a store opening in Brooklyn. "Commissioner Kelly has worked very hard coming up with the kinds of plans that we are going to use to protect this city."